Vehicles may recover exhaust heat for transfer to various other systems in an internal combustion engine.
For example, U.S. Pat. No. 7,832,204 describes a heat pipe system for an engine that allows for heat transfer between two or more different engine systems. The heat pipe system includes a boiler end that may transfer heat from a high temperature region to a condenser end at a low temperature region. The boiler end may be coupled to a region of the exhaust system and the condenser end may be coupled to another engine system, such as an engine coolant system, for transferring heat.
The inventors herein have recognized various issues with the above system. In particular, rapid heat at engine start is not available because the system requires the exhaust system to warm up first. Further, transferring heat away from the exhaust system during a cold start operation delays the catalytic converter ‘light-off.’ As a result, the catalytic converter does not operate at an efficient temperature to burn trapped hydrocarbons, thereby increasing exhaust emissions.
As such, one example approach to address the above issues is to use a heat pipe and suitable phase change materials to recover exhaust heat upstream and/or downstream from a catalytic converter. Further, heat may be stored for rapid use at engine start in terms of cabin heating and/or engine heating (through warming of engine coolant with the stored heat). In this way, it is possible to recover heat from the exhaust system via the stored heat, without adversely affecting a rate of reaching the catalytic converter light-off temperature, while at the same time providing more rapid cabin heating at cold engine starts and possibly more rapid engine heating (to reduce engine friction and thus improve fuel economy).
According to one embodiment, one or more heat pipes transfer excess exhaust heat to a closed thermosyphon loop, the loop including a phase change material housed within, and contained within, a heater core. During warmed up engine operation before engine shutdown, the one or more heat pipes transfer the excess exhaust heat to the thermosyphon loop, which in turn transfers the heat to the heater core to be stored in the phase change material within the heater core. Then, when the vehicle is shut-off, the phase change material in the heater core stores the heat for use during a subsequent engine cold start. During the cold start, airflow can be passed over the heater core to transfer heat from the phase change material to passenger cabin air, thus providing warm air to the vehicle's passenger cabin. Optionally, engine coolant can also be circulated in an engine coolant loop of the engine coolant system to the heater core to extract heat from the phase change material via heat transfer, which then enables warmed coolant to be returned to the engine to heat the cold engine and reduce engine friction.
Note that the heat transfer between the thermosyphon loop and the phase change material of the heater core may be through non-contact operation within the heater core, such as through a heat exchanger. Likewise, the heat transfer between the engine coolant loop (which is separate from the thermosyphon loop) and the phase change material of the heater core may be through non-contact operation within the heater core, such as through another heat exchanger in the heater core, if desired. Thus, in one example, the heater core may include three or more heat exchangers: one for heat transfer between the thermosyphon loop and the phase change material, one for heat transfer between the phase change material and passenger cabin air, and one for heat transfer between the phase change material and engine coolant.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.